The present invention relates in general to the field of hologram production and display and, more particularly, to a system and method for producing and displaying a one-step, edge-lit hologram.
Edge-illuminated or edge-lit holograms are considered to be a subcategory of holographic displays, in general. Typically, conventional edge-lit holograms are recorded onto a holographic recording material mounted on a material supporting substrate. The edge-lit hologram is then reconstructed by an illumination source that introduces an illumination beam through the edge of the substrate. The illumination beam preferably strikes the material supporting substrate at a steep angle relative to a light ray extending perpendicular to the surface of the substrate.
Edge-lit holograms contain interesting display properties. The holographic image can only be reconstructed with an illumination source introduced through the edge of the substrate. The illumination source is preferably disposed within the display. Thus, the display may be self contained which allows the holographic image to be protected from detrimental effects of ambient light sources. Some conventional systems place the illumination source relatively close to the edge-lit hologram. Additionally, some conventional systems integrate the illumination source with the edge-lit hologram in a stand-alone self-contained display. Such a system can eliminate the need for placement and adjustment of external illumination sources.
However, the recording and production of edge-lit holograms can be problematic. A typical hologram production system introduces an object beam carrying a digitally rendered image to coincide with a reference beam. The interference of the two beams forms a hologram on associated holographic recording material. To satisfactorily record the edge-lit hologram, the reference beam should approximate the high angle of incidence of the intended image reconstruction illumination source, taking into consideration optical characteristics of the material supporting substrate through which the eventual illumination source will travel. In general, a reference beam that sufficiently approximates such properties can be referred to as an xe2x80x9cedge-lit reference beam.xe2x80x9d
One conventional system for producing edge-lit holograms is disclosed in xe2x80x9cA Printer for Edge-Lit Holographic Stereograms,xe2x80x9d by Sean T. Nolan, which is a thesis submitted to the Department of Electrical Engineering Computer Sciences of Massachusetts Institute of Technology in February 1994. This reference documents a printer geometry that incorporates a reference beam introduced to a series of lenses that produce an anamorphically collimated reference beam with dimensions of approximately 25 millimeters by 0.4 millimeters. In order to condition the reference beam into an edge-lit reference beam, the disclosed device uses a plateholder consisting of a thick polymethylmethacrilate (PMMA) plinth and glass sandwich. The anamorphic or edge-lit reference beam is then introduced to the holographic recording material through the edge of the PMMA plinth.
This conventional production process is disadvantageous because the plinth is generally permanently laminated to the glass plateholder. Thus, the plinth must be approximately the same size as or larger than the hologram being recorded which typically limits the size of the hologram that the system can produce.
Another disadvantage of many conventional systems is introduction of the reference beam into an edge cut perpendicular to the face of the plate. This arrangement links the thickness of the PMMA plinth to the illumination angle of the hologram and further limits the size of the eventual hologram that can be produced.
A further disadvantage is that many conventional systems can not record full parallax edge-lit holograms and can not record full-color holograms.
One step hologram production technology has been used to satisfactorily record a hologram without the traditional step of creating a preliminary hologram. Both computer image holograms and non-computer image holograms may be produced by such one step technology. Also, not all computer image holograms are produced by one step technology. In some one-step systems, computer processed images of objects or computer models of objects allow the respective system to build a hologram from a number of contiguous, small, elemental pieces known as elemental holograms or hogels. To record each hogel on holographic recording material, an object beam is conditioned through the rendered image and interfered with by a reference beam.
In accordance with teachings of the present invention, a system and method are disclosed for producing and displaying a one-step, edge-lit hologram that provide significant advantages over prior edge-lit hologram production and display systems and methods.
According to one aspect of the present invention, a system for producing an edge-lit hologram comprises an object beam head, a reference beam head and a frame. The object beam head directs an object beam, and the reference beam head directs an edge-lit reference beam to interfere with the object beam. The holographic recording material and the object beam head and the reference beam head may then be translated in accordance with teachings of the present invention to record the hologram. The translation successively exposes multiple portions of the holographic recording material to interference of the object beam and the edge-lit reference beam to record an edge-lit hologram on the holographic recording material.
For one embodiment, the holographic recording material may be moved relative to the object beam head and the reference beam head which remain in a generally fixed position relative to each other. For another embodiment, the object beam head and the reference beam head may be moved in unison with respect to the holographic recording material which remains in a generally fixed position. For a further embodiment, the holographic recording material may be moved relative to the object beam and the edge-lit reference beam which are also moving substantially in unison with each other relative to the holographic recording material. For some embodiments, the reference beam head may comprise an assembly base and a prism coupled to the assembly base, where the prism is operable to receive the reference beam and condition the reference beam into an edge-lit reference beam.
Another aspect of the present invention includes a system for displaying an edge-lit hologram. The system preferably includes a base enclosure and a light source. The base enclosure may be formed to removably receive an edge of a plinth having an edge-lit hologram mounted thereon. The light source is preferably positioned within the base enclosure and provides an illumination beam to reconstruct the edge-lit hologram when the plinth is received by the base enclosure.
A technical advantage of the present invention is that the size of an edge-lit hologram to be produced is not limited to the size of the associated production optics. For example, a reference beam head incorporating teachings of the present invention may be used to record a hologram having dimensions substantially larger than the reference beam head.
Another technical advantage of the present invention is that an edge-lit reference beam does not have to be introduced into a perpendicular edge. Thus, the size of the edge-lit hologram to be recorded is not limited by the thickness of a plate or plinth having such an edge.
An additional technical advantage of the present invention is that either a horizontal parallax only or a full parallax edge-lit hologram can be recorded.
A further technical advantage of the present invention is that full-color edge-lit holograms may be recorded and displayed with substantially reduced color xe2x80x9ccrosstalk.xe2x80x9d
Still another technical advantage of the present invention is that multiple object beams and multiple edge-lit reference beams may be used to substantially increase the speed of printing an edge-lit hologram.
Another aspect of the present invention includes the use of one or more holographic optical elements (HOE) which may be placed along a respective edge of an edge-lit hologram opposite from an associated illumination source. Each HOE is preferably selected to function as a collimating mirror with respect to the associated illumination source which may be disposed adjacent to an opposite edge of the associated edge-lit hologram. Each HOE is selected to fold or reflect a beam of light from the associated illumination source at appropriate angles required for display of the associated edge-lit hologram. Placing an illumination source on one edge of an edge-lit hologram and an HOE on an opposite edge of the edge-lit hologram in accordance with teachings of the present invention will often allow a substantial reduction of the size or the length of the plinth or substrate used to support the edge-lit hologram.
Depending upon the type of image hologram which will be displayed, such as horizontal parallax only or full parallax, the present invention allows placing illumination sources and associated holographic optical elements at the desired location to minimize color crosstalk and to substantially reduce the size of the associated plinth and other components of the respective display systems.
A still further aspect of the present invention includes combining multiple color selective HOEs with corresponding colored illumination sources to substantially reduce or eliminate color crosstalk which is often associated with conventional techniques for illuminating edge-lit holograms. For example, a red illumination source may be disposed on a first edge of an edge-lit hologram and an HOE which is color selective with respect to collimating and reflecting a red light beam may be disposed on a second edge of the edge-lit hologram opposite from the first edge. In a similar manner a green illuminating source may be disposed on the second edge of the edge-lit hologram and an HOE selected to collimate and reflect green light may be disposed on the first edge of the edge-lit hologram. Each HOE is preferably transparent to any color other than the selected color which the HOE will collimate and reflect. For the above example the red HOE will reflect and collimate red light and will be effectively transparent to blue light, green light or any other color of light. The green HOE will reflect and collimate green light and will be effectively transparent to blue light, red light or any other color of light. The present invention allows placing colored light sources adjacent to selected edges of an edge-lit hologram to effectively reduce or eliminate color crosstalk.
The present invention teaches various techniques and apparatus for combining edge-lit hologram production with one step hologram production which makes possible the production of three dimensional hologram images that can be illuminated with an integrated light source to simplify and minimize the size of the resulting self-contained holographic display.
Other technical advantages should be apparent to one of ordinary skill in the art in view of the specification, drawings and claims.